Messages in this thread | | | From | Andy Lutomirski <> | Subject | Re: [PATCH] arch/x86: reset MXCSR to default in kernel_fpu_begin() | Date | Tue, 2 Jun 2020 12:50:42 -0700 |
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> On Jun 2, 2020, at 10:27 AM, Shuah Khan <skhan@linuxfoundation.org> wrote: > > On 6/2/20 11:03 AM, Andy Lutomirski wrote: >>> On Tue, Jun 2, 2020 at 3:56 AM Borislav Petkov <bp@alien8.de> wrote: >>> >>> Hi, >>> >>> On Tue, Jun 02, 2020 at 01:29:51PM +0300, Petteri Aimonen wrote: >>>> The kernel module is not actually x86-specific, even though it is >>>> currently only enabled for x86. amdgpu driver already does kernel mode >>>> floating point operations on PPC64 also, and the same module could be >>>> used to test the same thing there. >>> >>> Then make it generic please and put the user portion in, say, >>> tools/testing/selftests/fpu/ and we can ask ppc people to test it too. >>> People might wanna add more stuff to it in the future, which would be >>> good. >>> >>>> To deterministically trigger the bug, the syscall has to come from the >>>> same thread that has modified MXCSR. Going through /usr/sbin/modprobe >>>> won't work, and manually doing the necessary syscalls for module loading >>>> seems too complicated. >>> >>> Ok, fair enough. But put that file in debugfs pls. >> I think I agree. While it would be delightful to have general >> selftest tooling for kernel modules, we don't have that right now, and >> having the test just work with an appropriately configured kernel >> would be nice. > > Let's extend it to do what we want it to do. I will happy to take > patches. If you have some concrete ideas on what we can add, please > do a short summary of what is missing. I will find a way to get this > done. > >> How about putting the file you frob in >> /sys/kernel/debug/selftest_helpers/something_or_other. The idea would >> be that /sys/kernel/debug/selftest_helpers would be a general place >> for kernel helpers needed to make selftests work. > > Is this a workaround for the lack of selftest tooling for kernel > modules? In which case, let's us focus on fix selftest tooling.
The goal here is to have a selftest that runs kernel code as part of its operation. That is, the selftest is, logically, starting in userspace:
setup_evil_state(); ret = call_kernel_helper(); check_some_other_stuff(); undo_evil_state();
And the call_kernel_helper() could be moderately specific to the test.
> > thanks, > -- Shuah
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